The present invention relates to the field of microwave integrated circuits, and more particularly to a coplanar waveguide to slotline transition employing a slot cavity to provide broadband power transfer.
One type of microwave integrated circuit device is a coplanar waveguide which generally consists of a thin conductor formed on a dielectric substrate and has two parallel coplanar ground conductors on opposite sides of the thin conductor. A basic example of a coplanar waveguide 10 is illustrated in FIG. 1 and is shown to include a center conductor 12 and ground planes 14 and 16 formed on the surface of a dielectric substrate 18. The ground planes 14 and 16 are electrically isolated from the center conductor by the slots 17 and 19. A radio frequency ("RF") signal is generally provided to the coplanar waveguide 10 at signal input 20 of the center conductor 12.
Another type of microwave integrated circuit device is a slotline. A basic example of a slotline 22, shown in FIG. 2, includes a slot or channel 24 typically etched in an electrically conductive layer 25 formed on a dielectric substrate 26 to form separate electrically conductive regions 28 and 30. In the application of the slotline 22, an RF signal is generally applied to the conductive regions 28 and 30. The RF signal generates an electric field which extends across the slot 24 and a magnetic field which is perpendicular to a plane defined by the conductive layers 28 and 30.
Japanese Patent No. JA 2-20101 discloses a mode converting circuit for RF coupling a slotline to a microstripline. Such circuit includes a slotline fabricated on one side of an insulating substrate and a microstripline formed on the opposite side of the insulating substrate. The slotline, having a length 1, is coaxially aligned and contiguous with the microstripline, where 1 represents the corresponding wavelength of the RF signal of interest. A circularly shaped slot cavity fabricated on the slotline side of the substrate (the opposite side of the substrate on which the microstripline is formed) is used to couple the energy from the slotline to the microstripline.
Japanese Patent No. 53-79356 discloses a microstripline conversion circuit which is similar to the circuit described in Japanese Patent No. JA 2-20101. This circuit includes a microstripline fabricated on one side of a substrate which is RF coupled to a circularly shaped slot cavity fabricated on the opposite side of the substrate.
The circuits described in the above referenced patents are not coplanar, that is, all of the elements of these circuits are not formed on the same side of the insulating substrate. Thus, these types of devices are generally not very practical for applications involving microwave integrated circuits which require the bottom side of the insulating substrate to be a ground plane. Thus, there is a need for a coplanar waveguide to slotline transition where all of the active elements are located on one side of the substrate.
Therefore, there is a need for a microwave integrated circuit which is capable of transferring RF power between ground isolated circuities.